How do I inflate boat fenders to the correct pressure without damaging them?

Inflate your fenders gradually to the manufacturer's recommended pressure, using the correct valve adaptor and a gauge accurate at low pressure. Many conventional inflatable PVC fenders work at roughly 0.15 to 0.20 bar, or 2 to 3 psi, but your model's specified pressure takes priority, and the inflated fender should still yield under firm hand pressure.

Check the body and valve

Find the brand, model and inflation instructions, usually moulded into the body or available from the maker. Pressure limits and valve designs vary between manufacturers. Older fenders may have replacement valves.

Wash grit and salt from around the valve before opening it. Inspect the body, seams and rope eyes. Replace a fender with deep cracks, a distorted body or a torn attachment eye rather than adding air.

• Recessed valve with a removable screw plug: the plug may cover a separate inflation valve. Removing it does not necessarily leave a clear passage into the fender.
• Needle valve: use the specified smooth inflation needle, lubricated only as the maker directs.
• Proprietary valve: use the matching adaptor. A football needle is not a universal substitute.

Never force a needle or nozzle into an unfamiliar opening. It can tear the valve seal or push the valve into the body.

Choose a controllable pump

A hand or foot pump with the right adaptor gives good control. A bicycle pump can work if its connector accepts that adaptor, though its tyre-pressure gauge may barely register a fender's working pressure. Use a separate low-pressure gauge compatible with the valve, ideally with a range of around 0 to 5 psi and divisions of 0.1 to 0.2 psi.

A compressor can inflate a fender very quickly. Use one only if the manufacturer permits it, with a suitable regulator and adaptor. Add air in brief bursts. An ordinary tyre inflator's gauge may be inaccurate at these pressures.

Keep your face away from the valve and point it away from other people when adding or releasing air. A displaced plug or valve can cause injury.

Inflate in small stages

1. Move into the shade. Let a fender that has been lying in strong sunshine cool before judging its pressure.
2. Open the valve as instructed. Keep any cap or screw plug somewhere clean, and check its seal if fitted.
3. Fit the correct adaptor gently. Support the valve area so the pump hose cannot pull sideways on it.
4. Add a little air. Pause after a few strokes or a short burst, then check the pressure and shape.
5. Stop at the specified pressure. The body should reach its intended shape without bulging, stretched-looking seams or excessive hardness.
6. Remove the adaptor and refit the closure. Tighten it as instructed. Do not guess the torque or overtighten a plastic plug.